I'm a total glsl rookie trying to write a shader that gives you individual control over the four cornerpoints of your UV. Like the "Perspective Transform" image unit. But I can't get it to work. I realize I need something other then the texture2DRect call, but when I try to use texture2DProj it gives me errors. I guess I need a varying vec4 texcoord somehow, but how?
Any pointers in the right direction would be great.